var osp = document.getElementById("result");
function num(num){
osp.innerText=osp.innerText+num;
}
function cal(){
osp.innerText=eval(osp.innerText);
}
function delAll(){ 
	osp.innerText="";
}
function delLength(){
osp.innerText = osp.innerText.slice(0,osp.innerText.length-1);
}

